<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>弹性盒子</title>
  <link rel="stylesheet" href="flex.css">
</head>
<body>
  <div class="container">
    <div class="box1">div1</div>
    <div class="box2">div2</div>
    <div class="box3">div3</div>
    <div class="box4">div4</div>
  </div>
</body>
</html>